<h2>mach_port_request_notification</h2>
<hr>
<p>
<strong>Function</strong> - Request notification of the specified port event type.
<h3>SYNOPSIS</h3>
<pre>
<strong>kern_return_t   mach_port_request_notification</strong>
                <strong>(ipc_space_t</strong>                               <var>task</var>,
                 <strong>mach_port_name_t</strong>                          <var>name</var>,
                 <strong>mach_msg_id_t</strong>                          <var>variant</var>,
                 <strong>mach_port_mscount_t</strong>                       <var>sync</var>,
                 <strong>mach_port_send_once_t</strong>                   <var>notify</var>,
                 <strong>mach_msg_type_name_t</strong>               <var>notify_type</var>,
                 <strong>mach_port_send_once_t</strong>                <var>*previous</var><strong>);</strong>
</pre>
<h3>PARAMETERS</h3>
<dl>
<p>
<dt> <var>task</var> 
<dd>
[in task send right]
The task holding the specified right.
<p>
<dt> <var>name</var> 
<dd>
[in scalar]
The task's name for the right.
<p>
<dt> <var>variant</var> 
<dd>
[in scalar]
The type of notification.
<p>
<dt> <var>sync</var> 
<dd>
[in scalar]
Some variants use this value to overcome race conditions.
<p>
<dt> <var>notify</var> 
<dd>
[in notify send-once or receive (to be converted to send-once) right]
A 
send-once right, to which the notification will be sent.
<p>
<dt> <var>notify_type</var> 
<dd>
[in scalar]
IPC type of the <var>notify</var> right; either
<strong>MACH_MSG_TYPE_MAKE_SEND_ONCE</strong> or <strong>MACH_MSG_TYPE_MOVE_SEND_ONCE</strong>.
<p>
<dt> <var>previous</var> 
<dd>
[out notify send-once right]
The previously registered send-once right.
</dl>
<h3>DESCRIPTION</h3>
<p>
The <strong>mach_port_request_notification</strong> function registers a request for a
notification and supplies a send-once right that the notification
will use.  It is an atomic 
swap, returning the previously registered send-once right (or
<strong>MACH_PORT_NULL</strong> for none).  A notification request may be
cancelled by providing <strong>MACH_PORT_NULL</strong>.
<p>
The <var>variant</var> argument takes the following values:
<dl>
<dt> <strong>MACH_NOTIFY_PORT_DESTROYED</strong>
<dd>
<var>sync</var> must be zero.  The <var>name</var> must specify a receive right,
and the call requests a port-destroyed notification for the receive
right.  If the receive right were to have been destroyed, for instance
by <strong>mach_port_destroy</strong>, then instead the receive right will be
sent in a port-destroyed notification to the registered send-once right.
<p>
<dt> <strong>MACH_NOTIFY_DEAD_NAME</strong>
<dd>
The call requests a dead-name notification.  <var>name</var> specifies send,
receive, or send-once rights for a port.  If the port is destroyed (and the 
right remains, becoming a dead name), then a dead-name notification 
which carries the name of the right will be sent to the registered
send-once right.  If <var>sync</var> is non-zero, 
the <var>name</var> may specify a dead name, and 
a dead-name notification is immediately generated.
<p>
Whenever a dead-name notification is generated, the user reference 
count of the dead name is incremented.  For example, a send right with 
two user refs has a registered dead-name request.  If the port is
destroyed, the send right turns into a dead name with three user refs
(instead of two), and a dead-name notification is generated. 
<p>
If the name is made available for reuse, perhaps because of
<strong>mach_port_destroy</strong> or <strong>mach_port_mod_refs</strong>,
or the name denotes a
send-once right which has a message sent to it, then the registered send-once 
right is used to generate a port-deleted notification instead.
<p>
<dt> <strong>MACH_NOTIFY_NO_SENDERS</strong>
<dd>
The call requests a no-senders notification.  <var>name</var> must specify a
receive right.  If the receive right's make-send count is greater than or 
equal to the sync value, and it has no extant send rights, than an
immediate no-senders notification is generated.  Otherwise the notification is 
generated when the receive right next loses its last extant send right.  In 
either case, any previously registered send-once right is returned.
<p>
The no-senders notification carries the value the port's make-send 
count had when it was generated.  The make-send count is incremented 
whenever a send right is made directly from a receive right.  The
make-send count is reset to zero when the receive right is carried in a
message.
<p>
When moving a receive right, no-senders notifications are canceled, 
with a send-once notification sent to indicate the cancelation.
</dl>
<h3>NOTES</h3>
<p>
This interface is machine word length specific because of the port name
parameter.
<h3>RETURN VALUES</h3>
<dl>
<p>
<dt> <strong>KERN_INVALID_NAME</strong>
<dd>
<var>name</var> did not denote a right.
<p>
<dt> <strong>KERN_INVALID_RIGHT</strong>
<dd>
<var>name</var> denoted an invalid right.
<p>
<dt> <strong>KERN_INVALID_CAPABILITY</strong>
<dd>
<var>notify</var> was invalid.
</dl>
<p>
When using <strong>MACH_NOTIFY_DEAD_NAME</strong>:
<dl>
<p>
<dt> <strong>KERN_UREFS_OVERFLOW</strong>
<dd>
<var>name</var> denotes a dead name, but generating an immediate dead-name 
notification would overflow the name's user-reference count.
</dl>
<h3>RELATED INFORMATION</h3>
<p>
Functions:
<a href="mach_msg.html"><strong>mach_msg</strong></a>,
<a href="mach_port_get_attributes.html"><strong>mach_port_get_attributes</strong></a>.
